1. Field of the Invention
The present invention relates to a prism sheet and a backlight unit including the same. More particularly, the present invention relates to a prism sheet having a side which is perpendicular to the normal of a light guiding plate and a backlight unit including the same.
2. Description of the Related Art
A backlight unit provides a light to a liquid crystal display (hereinafter, referred to as “LCD”).
FIG. 1 is a block diagram illustrating a usual liquid crystal device.
In FIG. 1, the LCD includes a LCD panel 100 and a backlight unit 102.
The LCD panel 100 displays a certain image using a light provided from the backlight unit 102.
FIG. 2A is a sectional view illustrating a backlight unit. FIG. 2B is a sectional view illustrating an optical film of FIG. 2A.
In FIG. 2A, the backlight unit 102 includes a light source unit 200, a light guiding plate 206, a reflection sheet 208 and an optical film 210.
The light source unit 200 includes at least one cold cathode fluorescent lamp (hereinafter, referred to as “CCFL”) 202 and a reflection plate 204.
The CCFL 202 emits a light having a certain wavelength. Here, the light is generally a white light.
The reflection plate 204 seals the CCFL 202, and reflects the light emitted from the CCFL 202.
The light guiding plate 206 controls reflection condition of its upper side and lower side to diffuse uniformly the light emitted from the light source unit 200 through the whole light guiding plate 206. In addition, the light guiding plate 206 outputs the diffused light in the direction of the LCD panel 100.
The reflection sheet 208 reflects a light leaked from the light guiding plate 206 in the direction of the light guiding plate 206.
In FIG. 2A and FIG. 2B, the optical film 210 includes a diffusion sheet 220, a prism sheet 222 and a protection sheet 224.
The diffusion sheet 220 is located over the light guiding plate 206, and includes a lower diffusion sheet 230, a diffusion sheet base film 232 and an upper diffusion sheet 234. In addition, the diffusion sheet 220 includes beads 248, and condenses or diffuses the light outputted from the light guiding plate 206 using the beads 248.
The prism sheet 222 is located over the diffusion sheet 220, and includes a prism sheet base film 236 and prisms 238. Additionally, the prism sheet 222 condenses a light condensed or diffused by the diffusion sheet 220.
The protection sheet 224 is located over the prism sheet 222, and includes a lower protection sheet 240 includes beads 250, a protection sheet base film 242 and an upper protection sheet 246 includes beads 250. Further, the protection sheet 224 diffuses a light condensed by the prism sheet 222, and provides the diffused light to the LCD panel 100.
FIG. 2C is a sectional view illustrating the prism.
In FIG. 2C, the light outputted from the light guiding plate 206 is condensed by the prism 238. Then, the condensed light is transmitted in the direction of the LCD panel 100. However, a part (L4) of the light outputted from the light guiding plate 206 is not condensed in the direction of the LCD panel 100 as shown in FIG. 2C. In other words, the part of the light outputted from the light guiding plate 206 is not incident to the LCD panel 100, and so the efficiency of the light provided to the LCD panel 100 from the backlight unit 102 is reduced.